1. Field of Invention
The present invention relates to a technical field of an electro-optical device, such as a liquid crystal device, a manufacturing method therefor, and an electronic apparatus, such as a liquid crystal projector having the electro-optical device.
2. Description of Related Art
In general, an electro-optical device has a configuration in which electro-optic material, such as liquid crystal, is sandwiched between a pair of substrates, above one of which, pixel electrodes for pixels are provided so as to face the liquid crystal. In this case, the pixel electrodes are arranged in a matrix at a constant pitch (hereinafter referred to as “a pixel pitch” as appropriate). The surfaces of the pixel electrodes or the substrate surface that is in contact with the liquid crystal and the like are provided with an alignment layer for defining the operational state of the electro-optic material, such as the alignment state of the liquid crystal. In addition, each pixel electrode has a thin-film transistor (hereinafter referred to as a “TFT”) for controlling the switching of the corresponding pixel electrode, and the TFT has a scan line for supplying a scan signal and a data line for supplying an image signal. The opposing substrate, which is the other substrate of the pair of substrate, has an opposing electrode. During operation, a drive electric field is applied to the liquid crystal between the opposing substrate and the pixel electrodes whose switching is controlled by the TFTs to thereby drive the liquid crystal and the like for each pixel.
With this type of electro-optical device, when the substrate surface that faces the liquid crystal and the like has protrusions/depressions or steps, the operational state of the electro-optic material, such as the alignment state of the liquid crystal becomes unstable. Thus, since the scan lines, data lines, TFTs, and the like are fabricated in layers below the pixels electrodes above the substrate, if no measure is taken, such protrusions/depression or steps are generated because of the presence of those various wires and electronic elements.
Accordingly, a technique in which depressions are provided in the substrate and various wires and electronic elements are buried therein has been developed for reducing the protrusions/depression or steps that are generated at the substrate surface facing the liquid crystal and the like. In addition, a technique in which a CMP (chemical mechanical polishing) process is performed on the surface of an interlayer insulating film that is positioned at the uppermost layer and that serves as an underlying layer for the pixel electrodes has also been developed.
Meanwhile, this type of electro-optical device employs a row-direction inversion drive system (hereinafter referred to as a “1H inversion drive system”) in which the potential polarities for driving pixel electrodes are reversed for each pixel row for each field or a column-direction inversion drive system (hereinafter referred to as a “1S inversion drive system”) in which the potential polarities are reversed for driving for each pixel column, for the purpose of preventing a DC voltage from being applied to the liquid crystal and the like or preventing flicker. When such an inversion drive system is employed, lateral electric fields are generated between adjacent pixel electrodes. As a result, in the electro-optical device that is intended to be driven with longitudinal electric fields perpendicular to the substrate surface, a displayed image is disturbed in accordance with the strength of the lateral electric fields. Accordingly, in the related art, a technique have been developed for forming a protecting insulating film for reducing lateral electric fields in regions where no pixel apertures are provided along the scan lines or data lines, the regions being regions where lateral electric fields are generated. In the technique, depression portions are provided in the substrate and various wires and electronic elements are partially buried and not partially buried therein.
The related art technologies, however, cannot cope with steps caused by the presence of the pixel electrodes themselves. That is, steps in accordance with the film thickness of the pixel electrodes are generated at edges of the pixel electrodes that are provided in a plane with gaps therebetween. In addition, these techniques typically cannot cope with depressions that are generated in the surfaces of the pixel electrodes so as to correspond to the openings of contact holes for directly or indirectly connecting the pixel electrodes to the thin-film transistors.
Further, the steps in the vicinities of the edges of such pixel electrodes or depressions in the vicinities of the contact holes cause polyimide residues or the like to be generated or trapped when the alignment layer formed of polyimide or the like on the pixel electrodes is rubbed. In addition thereto or in place thereof, the residues may be suspended in the liquid crystal in a process after rubbing. The material residues from the alignment layer pose a technical problem in brightness irregularities or display irregularities occur in an image eventually displayed.
In particular, as the pixel pitch is further reduced so as to meet a general requirement for displaying a higher-definition image to further reduce the gap between the substrate, the steps or depressions in the vicinities of the contact holes due to the presence of the pixel electrodes relatively become large. On the other hand, a reduction in the pixel pitch causes the size of the polyimide residues or the like to increase relatively. Thus, the technical problem due to such residues generated or trapped in the vicinities of the edges of the pixel electrodes or in the vicinities of the contact holes and due to residues suspended in the electro-optic material becomes more severe.